High frequency transmitter



July 4, 1933. -w. LANGEWIESCHE 1,916,843

HIGH FREQUENCY TRANSMITTER Filed Sept. 20, 1930 INVEli TOR 9 Wilhelm Langeun'csche Patented July 4, 1933 warren stares Parser easier:

VTILHELM LANG-EXVIESCHE, E EFFlTUV-TFT-FPFET T 01 GWT WfA TY, ASSIGN'OR 0F FIFTY PER CENT 'I'G RADIO PATENTS CGRLORATION, OF NEVJ' YORK, N. Y.

HIGH FREQUENCY TRANSMITTER Application filed September 20, 1930, Serial No. 483,241, and in Germany September 21, 1929.

My invention relates to high frequency generators and more particularly to means for modulating the oscillations of a high frequency vacuum tube oscillator in accordance 5 With varying signal currents, or currents of other nature which it is desired to transmit by means of the high frequency carrier oscillations. A

An object of my invention is to provide an improved circuit for a high frequency transmitter which, with the employment of a-minimum of circuit elements, insures increased e-tficiency and dependability of operation.

Another object of my invention is to provide a high frequency vacuum tube transmitter which may be easily operated and which requires little attendance and low maintenance cost.

v A more specific object of my invention is to provide means in connection with a vacuum tube oscillator for transmitting high frequency signals in which an auxiliary vacuum tube, preferably the modulating tube of the oscillator, is heated by a part of the high frequency oscillating energy of the os cillator.

These and further objects of my invention will become more apparent as the following description proceeds, taken with reference to the accompanying drawing in which I have illustrated a number of embodiments of my invention which it is understood is subject to many modifications and variations coming within the broad inventive principle as expressed by the appended claims.

Figure 1 shows schematically a well-known circuit arrangement of a radio oscillator including a master oscillator and power oscillator and a grid current modulating arrangement to which my invention has specific reference.

Figure 2 is a circuit illustrating one embodiment of the invention.

Figure 3 illustrates an alternative method of practicing the invention similar to Figure 2.

Figures 4, 5, and 7 show further arrange ments according to my invention in. which part of the oscillating current serves to heat the filament of the modulating tube.

Figure 6 is an arrangement in which a separate storage battery isprovided for supplying heating energy of the modulator.

Similar reference numbers refer to similar parts throughout the different views of the drawing.

It is customary to modulate the high frequency oscillations of a discharge tube oscillator according to a system well known as direct current grid modulation which I have illustrated for purposes of clearer understanding in Figure 1 of the drawing. Referring to this figure I have shown a master oscillator comprising a three-electrode vacuum tube connected with an oscillatory circuit 2 in the well-known Hartley connection for producing high frequency oscillations. The oscillations are transmitted to an intermediate circuit comprising a self inductance 3, a variable capacity 4, and a further self inductance 5. From this circuit the oscillations are applied to the grid of the power amplifier tube 6 in a manner well known. This tube also serves for modulating the oscillations in accordance with signalling currents which it is desired to impress on the high fre quency carrier for transmission such as by wireless or across a connecting line. The modulation is carried out by the modulating tube 7 having its cathode connected to the grid of the power amplifying tube 6 in series with a choke coil 8, and having its anode connected to the cathode of the power amplifier. The modulating currents, such as for instance microphone currents when the oscillator is used as to radio phone transmitter, or the picture currents when the oscillator is used in a picture transmitting system, are applied to the grid of the modulating tube 7 across an input transformer 9.

In such a system as described, it is necessary to provide a separate heating battery 10 for the filament of the modulating tube 7 which is at a relative potential in respect to the cathode of the power amplifier normally of about several hundred volts and which, therefore, has to be insulated carefully from the remaining current sources of transmitter and service interruptions on account of unforseen exhaustion of the battery, will frequently occur. Wheuusing generators for supplying the heating current for the modulating tube, 1t 1s necessary to use 10 special constructions insuring freedom from harmonics and being provided with high tension insulation. Furthermore, generators require expensive means for the elimination of disturbing noises such as filters and choke 15 coils, thus considerably increasing the first cost as well as the operating expenses of the transmitter. This has always been felt as being a great inconvenience in high frequency transmitters of this type.

I haveshown furthermore a resistance 11 connected in the intermediate circuit 3, 4,

which serves for increasing the damping of the circuit and accordingly for'preventing the production of self oscillations of the power amplifying tube, and for decreasing the reaction of the power amplifier tube upon the master oscillator.

Referring more particularly to Figure. 2 which illustrates one embodiment of the invention; thisshows a direct current grid modulation circuit according to which the modulating tube has its'cathode connected directly to a point of the high frequency circuit the oscillations in which are applied to the power amplifying tube. The anode ofthe modulating'tube isconnected to the cathode of the power amplifier. Such a con nection presents many advantages as compared to the older circuit described in Figure 1, in that part of the circuit elements according to Figure 1 may be entirely dispensed with or substituted by simpler devices as will become obvious.

According to Figure 2 the heating battery for the modulating tube has been avoided and thus the inconveniencesas pointed out primarily due to its insulated position from the remaining parts of the transmitter, have been completely overcome.

The heating energy for the modulating tube is supplied from the highfrequency circuit 3, 4, 5 in that the high frequency oscillating current passes through the filament and serves to maintain the same at a temperature necessary for electron emission. Onaccount of the high frequency of theheating current, no disturbing note or hum will be-observed in the output of the transmitter such as is the case when heating the filament with power frequency currents as supplied from the powernet works or also when using medium frequencies for heating supplied by a special generator. In the latter cases, means have to be provided for smoothing out the irregularities orripples in the heating cur-v rent and it is obvious that the use of high frequency currents, according to this invention, constitutes a great advantage in that there is no necessity for additional smoothing devices. The connection, according to Fi ure 2, furthermore provides a considerable damping of the circuit 3, 4, 5 on account of the ohmic resistance of the filament of the modulating tube and thus in most cases I simplicity is desired.

In order not to put an unnecessary load on the modulating tube, it is preferable to provide a high frequency short circuit such as by means of a shunt consistingof the capaci y ora combination of a capacity 13 and a self inductance 14 in parallel to the modulating tube, as illustrated in the drawing. Preferably this shunt circuit 13, 1a .is tuned to the frequency of the high frequency currents. I

It is also possible to increase the resistance of the modulating tube presented to the high frequency currents by means of-a series choke coil 15 in the anode circuit in which case a single capacity 13 may serve as a shunt for the high frequency currents. If desired, high frequency chokes 16 and 17 for the voice or. control currents may be inserted in the leads from the transformer 9 in a manner well known. I

It has furthermore been found advantageous, in order to keep the reaction of the power oscillator upon the master oscillator at a minimum, to supply the high frequency grid control voltage for the tube 6 not from the entire coil 5 but to provide a suitable tap such as indicated in Figure 3 or to insert an additional self inductance in the circuit 3, 4, r

. hen using the ordinary modulating tubes available on the market, it is in most cases possible to connect the heating filament direct-lyin the high frequency circuit, as described in connection with Figures 2 and 3.:

If, however, the heating current of the modulating tube'has a different intensity from the oscillating current, a resistance 19 inserted in the high frequency circuitand connected in parallel to the filament,may be provided as shown in Figure 7,'orthe tube may be heated by an auto-transformer arrangement consisting of an inductance coil 18 in series with the high frequency circuit as shown by-Figure'al.

Referring to Figure 5; this illustrates an example in which the heating filament of the modulating tube ismserted 111 the 1ntermedlate circuit of the master osclllator. The

I secondary circuit comprisesself inductance 3, self inductance 20, variable capacity 21, self inductance 14, and capacity13. I 13 and 1 1 are tuned to the frequency of the transmitting wave length in such a manner that the modulating tube is connected to points of the oscillating circuit which are at zero potential difference in respect to the high frequency oscillations. It is, of course, also possible to connect the heating filament in the secondar circuit 3, 20, 21, 14:, 13, or also in the common coupling path between the primary and secondary circuit, or, in general, in any circuit carrying high frequency current. The high frequency voltage in this arrangement is capacitatively applied to the grid of the power amplifier 6 whereby parasitic oscillations of short wave length, as they occur incidentally when using an inductive connection, are suppressed to a large extent. In order to separate the grid of the power tube from the grid or filament of the controlling or master tube, a blocking condenser 22 is inserted, as shown.

In Figure 6 I have illustrated a. further connection in which a battery is provided for heating the filament of the modulating tube. According to this circuit the three high frequency choke coils 15, 16, 17 are substituted by a single choke coil 23 connected between the cathode of the modulating tube and'the oscillatory circuit 3, 4, 5. The modulating tube and the choke are bridged by a shunting capacity 13.

Referring to the arrangement according to Figure 7 in which the grid condenser 12 has been retained, a special path is provided for the direct grid current by means of a choke coil 24 connected between cathode of the modulating tube and the grid of the power amplifier tube. The filament of the modulating tube is shunted by a resistance 19 for decreasing of the heating current, as already described.

Although I have illustrated my invention with specific reference to the showing of a master oscillator-power oscillator combination for which the invention is primarily suited, it is obvious that the general principle as expressed in the following claims may be applied to any kind of arrangement coming within the broader scope of the art to which the invention appertains.

lVhat I claim is:

1. In combination with a telephone transmitter, a master oscillator generating high frequency currents, a power amplifying tube controlled by said master oscillator, a modulating tube having its filament inserted in the output circuit of said master oscillator to be heated by said high frequency current and having its anode connected to the oathode of said power amplifying tube and a high frequency shunt between the cathode and anode of said modulating tube.

2. In a telephone transmitter, as described in claim'l, in which said shunt consists of a capacity and inductance in series and tuned to the frequency of said high frequency currents.

' 3. 'Incombination with a telephone transmitter, a master oscillator generating high frequency currents, an output circuit of said master oscillator, a power amplifying tube having its grid'connected to a point of said circuit, amodulating tube having its filament inserted in said output circuit to be heated by said high frequency current and having its anode connected to the filament of said power amplifying tub-e, an impedance between the anode of said modulating tube and the filament of said power amplifying tube, and a shunting capacity between the cathode and anode of said modulating tube.

4. In combination with a telephone transmitter, a master oscillator generating high frequency currents, an output circuit of said master oscillator, a power amplifying tube having its grid connected to a point of said output circuit, a modulating tube having its filament connected to taps on said circuit to be heated by said high frequency currents and having its anode connected to the fila ment of said power amplifying tube.

5. In combination with a high frequency transmitter, a master oscillator generating high frequency current, an output circuit of said master oscillator, a power amplifying tube, a coupling condenser connected between the grid of said power amplifying tube and a point of said output circuit, an impedance in said output circuit, a modulating tube having its filament connected to the ends of said impedance, and having its anode connected to the filament of said power amplifying tube, a high frequency shunt for said impedance and said modulating tube, and a further impedance providing a direct current path between the filament of said modulating tube and the grid of saidpower amplifying tube.

6. In a high frequency transmitter comprising a master oscillator; a power amplifying tube having cathode, anode and grid electrode controlled by said master oscillator; means including a modulating tube for applying modulating potential to the grid electrode of said power amplifier; and means for heating the cathode of said modulating tube by high frequency energy supplied by said master oscillator.

7. In a high frequency transmitter comprising a master oscillator; an output circuit of said master oscillator; at least one power amplifier tube having cathode, anode and grid electrode controlled by said master oscillator; amodulating tube having incandescent g of said power amplifier in accordance with cathode, grid" and anode electrode controlling the grid ofsaid power amplifier-in accordance with modulating signals, the cathode of said modulating'tubebeing inserted in the output circuit of said masteroscillator to be heated by the high frequency currents;

8. In a high frequency transmitter comprising a master oscillator; an output circuit of said master oscillator; a power amplifier having cathode, anodeand grid electrode controlled by said master oscillator;a modulating tube having cathode, "d, and anode electrode connected to'vary t e grid current modulating signal impulses; the heating'filament of said modulatingv tube being'connecbed with said master oscill ator output circuit:

to beheated by a portion of the oscillating current in said masteroscilla-ting circuit.

9. The combination with a radio trans- 'mitter, a master oscillator generating high ILHELM LANGEWIESCHE. 

